It is well known in the art to use glass fibers as reinforcements in the manufacture of molded polymeric composites. Glass fibers do not shrink or stretch in response to changes in atmospheric conditions and thus provide dimensional stability to the resulting composite. Further, the high tensile strength, heat resistance, moisture resistance, and thermal conductivity of glass fibers can improve the mechanical properties of the composite as well.
Glass fibers are commonly manufactured by supplying glass in molten form to a bushing, drawing fibers from the bushing, and then gathering the fibers into a tow or strand. A sizing composition, or chemical treatment, is typically applied to the fibers after they are drawn from the bushing to protect the fibers from breakage during subsequent processing, and to improve the compatibility of the fibers with the matrix resins that are to be reinforced. The sized strands are then typically chopped into lengths suitable for dispersing throughout a matrix resin to form a molding compound that can be molded into shaped composite articles. The strands may be chopped wet or dry (i.e., before or after the sizing composition dries) and the resulting strand segments may be densified and combined to form pellets, if desired. The strand segments or "chopped strand" is then typically dispersed throughout the matrix resin via an extrusion operation commonly referred to as compounding, to form a molding composition that can be molded into fiber-reinforced composite articles.
The size compositions applied to the fibers to reduce interfilament abrasion and improve the chemical coupling between the fiber and the polymer matrix typically comprise one or more film-forming polymeric or resinous components, lubricants and glass-resin coupling agents dissolved or dispersed in water. However, in addition to improving the processability of the fiber and the fiber-polymer coupling, the sizing composition should also enhance the wetting of the individual fibers by the matrix resin.
Accordingly, in view of the dual role of the sizing compositions in improving processability of the fibers while improving the physical properties of the resulting composite, as well as the vast variety of polymeric materials that can be advantageously reinforced with glass fibers, a continuing need exists for specifically tailored sizing compositions that provide enhanced physical properties and appearance to articles molded from specific polymeric matrix materials.